I was thinking that he may have been part of a smuggling ring quietly smuggling Polonium 210 etc. on behalf of Russia to destinations such as Iran. The dirty bomb idea occurred to me towards the beginning of my thinking on an alternative theory on Litvineko's death. The following from Epstein's website changed everything:
"Then there is the polonium 210 used to explode the bomb. The AIEA determined that Iran has obtained polonium 210, an isotope. And the likely source is Russia, which uses it (in combination with beryllium) to ensure the chain reaction leading to a nuclear explosion begins at the right time."
http://www.edwardjayepstein.com/2003question/IransWMD.htm
I would think it at least deserves a thorough looking into at the very minimum.
Smuggling to iran from russia needs not to be done through England [why not New Zealand as a transit point?]- they share a water border in Caspian. Simpler, easier, no prying eyes, less possibility for the things going awry. As William of Occam used to say, "thou shalt not complicate". Why scratch one's left ear with the right hand from behind over one's groin?